Process of hydrophilization, purification and bleaching of cellulose fibers

ABSTRACT

Cellulosic materials, such as cotton fibers or mixtures of cotton and other cellulosic or synthetic fibers, are hydrophilized, purified and bleached by treating the cellulosic materials with a small amount of chlorine dioxide over a short period of time and then bleaching the treated cellulosic material with a peroxidized compound.

FIP8309 United States Patent 1111 3,619,110

172 Inventor Roger Jullen Borezee 156] Relerences Cited L8 Celle Saint-Clous. France UN|TED STATES PATENTS QY J- $323 1.580.136 4/1926 Hamburger et 11. 8/109 x 3% f d 9 197] 2,494,542 1/1950 Casciuni et 111 8/109 x ?""f k m 2.526.839 10/1950 AS1011 8/109 x I I 55: f g 3.345.250 10/1967 Brinkley. Jr. et 111.. 81/109 x Priority 0c!- 22 I968 3.481.684 12/1969 Sando et a1. 8/109 X 33 1 France Primary Examiner- Mayer Weinhlatt [31 170,805 Almrney-Pennic, Edmonds, Morton. Taylor and Adams [54] PROCESS OF HYDROPI-IILIZATION,

PURIFICATION AND BLEACHING 0F CELLULOSE FIBERS 7 Clams No Drawmgs ABSTRACT: Cellulosic materials, such as cotton fibers or [521 U.S. Cl 8/109, mixtures of cotton and other cellulosic or synthetic fibers, are 8/101, 8/1 1 l, 162/78 hydrophilized, purified and bleached by treating the cellulosic [51 Int. Cl D061 3/06 materials with a small amount of chlorine dioxide over a short [50] Field 01' Search 8/109, 101, period of time and then bleaching the treated cellulosic 111; 162/78 material with a peroxidized compound.

PROCESS OF I-IYDROPI-IILIZATION, PURIFICATION AND BLEACHING OF CELLULOSE FIBERS BACKGROUND OF THE INVENTION A high degree of hydrophily or water absorbency is desired in articles made from cellulosic materials, such as cotton, in order to facilitate dyeing, notably in pad dyeing, printing, to facilitate the penetration of finishes and so fourth. This high degree of water absorbency is also desired when the cellulosic article is intended for surgical use, such as surgical gauze.

In addition, the dyeing of cellulosic materials with dyes that react with the cellulose and the finishing techniques employing thermosetting resins require that the cellulosic materials be quite purified and substantially free of noncellulosic matter that might interfere with the fixing of these dyes or reactive finishes such as the thermosetting resins.

The usual process of hydrophilization and purification of cellulosic materials involves an alkaline cooking at elevated temperatures and at times above atmospheric pressure, followed by a bleaching of the cellulosic material with a peroxide compound, such as hydrogen peroxide, sodium chlorite or sodium hypochlorite.

Even though such a process produces substantially purified and hydrophilic materials, the process has a number of disadvantages. For example, the alkaline cooking, which hitherto has been considered the most effective and most economical means of eliminating noncellulosic impurities, has the drawback of weakening the cotton fiber, altering its surface properties and sensitizing it to the oxidizing bleaching agents; moreover, after an alkaline treatment the bleached fibers often have mechanical properties inadequate for the application of certain finishes, which themselves further affect their strength. Furthermore, to be truly effective, alkaline cooking must be carried out at an elevated temperature and over a sufficiently long period, so that the fatty substances of the cotton can be saponified. Admittedly, this time can be shortened by working at high temperatures (l30 C., for example), but this means that autoclave equipment must be available. Thus, one of the chief disadvantages of this process is the duration of the alkaline cooking and bleaching reactions which makes it difficult to treat (particularly by continuous application techniques) delicate fabrics, such as satins and poplins, which do not readily tolerate prolonged mechanical stress.

SUMMARY OF THE INVENTION The present invention relates to a new process for treating cotton articles or mixtures of cotton and other natural or synthetic cellulose fibers that results in a cotton article having excellent hydrophilic properties, a high degree of purification and a high degree of whiteness without significantly affecting the cellulose in a very short period of time.

The process in accordance with the invention comprises treating the cellulosic material with chlorine dioxide followed by bleaching with a peroxidized product, such as hydrogen peroxide, sodium peroxide, sodium chlorite or sodium hypochlorite.

The cellulosic materials that can be treated according to this invention include cotton or mixtures of cotton with other cellulosic materials, such as regenerated cellulosic materials or mixtures with synthetic materials, such as polyester-cotton and viscose rayon-cotton mixtures. These cellulosic materials may be in the form of floss, silver, laps, yarn or cloth. The term cellulosic materials are used herein is therefore intended to include mixtures of cellulosic materials and the various forms thereof, such as set forth above.

if the cellulosic materials, such as cloth, are sized, it is advantageous to first desize the cellulosic material prior to treating the cellulosic material in accordance with this invention. This desizing can be effected by a number of known processes, such as by diastases (amylolytic enzymes) alkali persulfate or alkali bromite. If the cellulosic materials are to be continuously treated, the desizing operation could be effected by passing the cloth for a minute through the tank of a washing machine containing a concentrated solution of amylolytic diastase or enzyme followed by a vigorous washing to remove traces of hydrolized starch.

The pretreatment of the cellulosic materials with chlorine dioxide prior to the bleaching operation constitutes an essential step of the invention. The treatment with chlorine dioxide involves contacting the cellulosic material with a small amount of chlorine dioxide in the gaseous state or in solution for a very short period of time. If the chlorine dioxide is used in the gaseous state, it is advantageously diluted with air or inert gas, such as nitrogen, for example, and can be applied by passing the cellulosic material which had been previously moistened with water through a chamber containing the gaseous medium in proportions so that the cellulosic material picks up between about 0.05 to 0.5 percent by weight chlorine dioxide under the particular operating conditions employed. The temperature and residence time of the cellulosic material in the chamber containing the diluted chlorine dioxide gas can be varied, depending upon the particular concentration of the chlorine dioxide gas contained therein, the form of the cellulosic material, as well as the type of cellulosic material, as will be apparent to those skilled in the art. Generally, the temperature in the chamber when the diluted chlorine dioxide gas is used can be between about 10 and 130 C. and the residence times can vary from between a few seconds to about 30 minutes.

The cellulosic materials can also be treated according to this invention with an aqueous solution of chlorine dioxide by soaking the cellulosic material in the chlorine dioxide aqueous solution. Ordinary bleaching and dyeing equipment, such as vats, jiggers, washing machines, and so forth, can be used for treating the cellulosic materials with chlorine dioxide in aqueous solutions. The chlorine dioxide aqueous solution can also be applied to the cellulosic materials by impregnation with foulardage and then let the cellulosic material stay in equipment of the J-box-type, a pad-roll-type maturation chamber, or any other suitable accumulation system. The application of the chlorine dioxide to the cellulosic material can also be carried out in an autoclave to permit heating to higher temperatures and at pressures of from about 1 to 4 atmospheres if this ever becomes desirable.

When utilizing an aqueous solution of chlorine dioxide. the amount of chlorine dioxide used should result in a pickup on the cellulosic material of from about 0.05 to 0.5 parts by weight of chlorine dioxide per parts of the textile material during its passage through a residence in the chlorine dioxide containing aqueous solution under the particular operating conditions employed.

When using an aqueous solution of chlorine dioxide, the pH of the solution, its temperature, and the pressure employed may be varied as will be apparent to those skilled in the art. It has been found to be advantageous, however, to use an aqueous solution of chlorine dioxide having a pH of between about 2 and 7 and to carry out the process at a temperature of between about 10 and l30 C. The cellulosic material can be passed through a hot solution of chlorine dioxide or, if desired, it can be immersed in a cold solution of chlorine dioxide. and the temperature of the solution raised to the desired temperature. For example, in the pad processes the cellulosic material can be impregnated with a cold solution of chlorine dioxide and after drying or-removal of excess solution, the cellulosic material can be heated with steam or some other heating system and placed in a J-box for a period of time which can vary from a few seconds to-30 minutes, depending upon the particular cellulosic material being treated and the process conditions.

in general, since the amount of chlorine dioxide applied to A the textile is very small, the reaction with the waxy substances of the cotton and the reducing substances is extremely rapid and it is possible to envisage very short treatments on ordinary equipment without fear of the drawbacks inherent in the application of current methods of bleaching with chlorine dioxide. In most cases amounts of chlorine dioxide of the order of from 0.1 to 0.3 percent relative to the weight of the cotton are sufficient to prepare the fiber for bleaching. Such quantities are not enough to bleach natural cellulose fibers, but they are enough to oxidize the fatty substances and noncellulosic impurities which help to give these fibers their hydrophilic character.

After pretreatment with chlorine dioxide the textile is treated, with or without intermediate washing, with the peroxide bleaching solution. Apart from peroxide, the latter contains the usual alkaline agents: caustic soda and sodium carbonate, the usual stabilizers: sodium silicate and magnesium silicate, and/or organic sequestrants, such as, ethylenediamine tetracetic or diethylenetriamine pentacetic acid and their alkaline or alkaline-earth salts. Bleaching can be effected in ordinary equipment kiers with or without pressure, vats, jiggers, impregnation tanks and any thermal accumulation system of the J-box and pad-roll types or in equipment for pressure bleaching in a steam medium. The duration of bleaching with hydrogen peroxide can vary but generally takes between a few minutes and 30 minutes. The temperature at which bleaching is carried out can also vary and can generally lie between 80 and 140 C.

This peroxide bleaching following treatment with chlorine dioxide is another important step of the invention. In particular, it is the combination of the two treatments that make it possible to obtain the excellent hydrophilic property of the cellulosic materials treated in accordance with the process.

The following examples illustrate the present invention. To avoid disturbing the hydrophilic measurements no surface-active or wetting agent has been used in any of the operations.

DETAILED DESCRIPTION OF THE INVENTION EXAMPLE I Combed cotton was plunged for 3 minutes into a solution containing 0.1 g. chlorine dioxide per liter and brought to pH 4 with acetic acid. The amount of solution represented 20 times the weight of the cotton and thetemperature of the solution was 90 C.

The same cotton was then plunged into a solution containing 1 percent hydrogen peroxide, 1 percent caustic soda, and 1.5 percent liquid sodium silicate at 36 Be relative to the weight of the cotton.

The temperature of this solution was 95 C. and the ratio of material to bath 1:10. The temperature was kept at 95 C. for 30 minutes, after which the cotton was thoroughly rinsed with hot then cold water.

No wetting agent was used in the course of these operations. Once dry, the hydrophily or water absorbency of the cotton was checked by the method described in the Codex Francais. This method consists in carefully depositing on the free surface of a body of water contained in a l-liter crystallizer a square of cotton measuring 2 cm. along the side and weighing about 0.25 g., and then measuring the time that the square of cotton takes to sink into the water. Cotton treated in accordance with the invention became soaked in 2 seconds, whereas another specimen that had only been bleached with hydrogen peroxide without a preliminary treatment with chlorine dioxide took 133 seconds to become soaked.

EXAMPLE II An Egyptian cotton cloth, previously desized with malt diastase and washed in boiling water, was impregnated at the ambient temperature with a chlorine dioxide solution prepared by the action of sulfuric acid on a sodium chlorite solution and containing 2 g. per liter of chlorine dioxide. The cloth was then dried by passing between the rolls of a pad so that it retained only its weight of liquid, after which its temperature was rapidly brought to 100 C. by passing it through a steam-heated chamber. It was then stored for 5 minutes in a thermally insulated J-Box. The cloth was then washed in cold water, then squeezed out and impregnated with a cold solution of hydrogen peroxide containing, in addition, caustic soda and sodium silicate. The concentration of this solution and the degree of squeezing (drying) of the cloth were so calculated that, after passing between the rolls of the foulard. there remained on the cloth 1 percent hydrogen peroxide, 0.5 percent caustic soda, and 2 percent sodium silicate at 36 Be relative to the weight of the cloth.

The latter was heated by passing through a steam-filled chamber and then kept for 10 minutes in the J-Box. Finally it was washed first in hot, then in cold water.

The hydrophilic property of the cloth was checked by the ASA method No L 14115-1961 which consists in letting a drop of water fall from a buret fixed 1 cm. above the stretched surface of the cloth and in measuring the time taken by the textile to absorb the drop. Cloth treated as described above absorbs the water in 2 seconds (mean of 20 tests) whereas the same cloth which had only been desized before being treated with hydrogen peroxide only absorbed the water in l 14 seconds (means of 20 tests). By way of comparison a sample of the same cloth desized, boiled in soda, and then bleached with peroxide absorbs the water in 6 seconds.

The degree of whiteness, measured with the Zeiss Elrepho electrophotometer using a 457p. filter, was 82.2 (relative to a magnesium oxide standard) for the cloth pretreated with chlorine dioxide and 80.1 for the nonpretreated cloth. The degree of polymerization of the cloth pretreated with chlorine dioxide was 1,830, that ofthe nonpretreated cloth 1,850.

EXAMPLE III The operations described in example II were applied to the same type of cloth but in a high-temperature vaporizer in which the cloth stayed for 30 seconds at 130 C. for the pretreatment with chlorine dioxide and for seconds at C. for bleaching with hydrogen peroxide.

I-Iydrophilic tests gave a time of less than 1 second (mean of 20 tests) for the cloth pretreated with chlorine dioxide to absorb the drop of water, whereas the nonpretreated cloth took 8 seconds (mean of 20 tests).

The degree of whiteness of the pretreated cloth was 80.4 as against 78.6 for the nonpretreated cloth and the degrees of polymerization were 2,060 for the pretreated cotton and 2,040 for the nonpretreated cotton, respectively.

EXAMPLE IV Raw wet carded cotton with a moisture content of percent was placed in a heated chamber at 70 C. in which a stream of air containing 4.3 percent chlorine dioxide by volume was caused to circulate. The amount of chlorine dioxide introduced into the chamber was 0.18 percent relative to the weight of the dry cotton.

After 2 minutes all of the chlorine dioxide was found to have disappeared. The cotton was then impregnated with its own weight of a solution of hydrogen peroxide, like that used in example 1, and placed in a chamber into which steam was injected to raise the temperature to 98 C. After heating for 30 minutes, the cotton was washed with water at 60 C., then with cold water, and dried. It was perfectly white and when tested by the Codex Francais method became soaked in 2 to 3 seconds.

I claim:

1. A process for obtaining cellulosic materials or mixtures of cellulosic materials and synthetic fibers characterized by improved hydrophilic properties, purity and whiteness, comprising treating the cellulosic material with an amount of chlorine dioxide sufficient enough and for a period of time long enough to hydrophilize the cellulosic material but not to bleach the cellulosic material and then bleaching the cellulosic material with hydrogen peroxide, sodium chlorite, sodium hypochlorite or sodium peroxide.

2. The process of claim 1 in which the chlorine dioxide is used in an amount of from about 0.1 to 0.3 percent by weight of the cellulosic material to be treated.

the cellulosic material.

6. The process of claim 1 in which the treatment with chlorine dioxide is effected at temperatures in the range from 10 to C.

7. The process of claim 1 in which the reaction time of the chlorine dioxide treatment varies between a few seconds and 30 minutes. 

2. The process of claim 1 in which the chlorine dioxide is used in an amount of from about 0.1 to 0.3 percent by weight of the cellulosic material to be treated.
 3. The process of claim 1 in which the chlorine dioxide is used in the form of an aqueous solution having a pH between about 2 and
 7. 4. The process of claim 1 in which the chlorine dioxide is used in gaseous form, diluted with air or an inert gas.
 5. The process of claim 1 in which the treatment with chlorine dioxide is effected under conditions, such that from about 0.05 to 0.5 percent of the chlorine dioxide is fixed on the cellulosic material.
 6. The process of claim 1 in which the treatment with chlorine dioxide is effected at temperatures in the range from 10* to 130* C.
 7. The process of claim 1 in which the reaction time of the chlorine dioxide treatment varies between a few seconds and 30 minutes. 